The present invention relates to the monitoring of a cooling system and, in particular, relates to an apparatus and method for measuring and monitoring critical parameters of a chiller unit in real-time.
For a cooling system to operate smoothly and cost-effectively, it must run efficiently. There are many factors, however, that can affect the cooling system's efficiency. For example, an overburdened cooling system may be the result of scale build-up, fouling, corrosion, or impeded heat transfer or machine operation stemming from improper flow rates or refrigerant charge.
There have been apparatus and methods proposed which analyze some aspects of a cooling system's operation. For example, U.S. Pat. No. 4,768,346 issued to Mathur discloses a method for calculating the coefficient of performance (COP) of a vapor compression type refrigeration system. Specifically, COP algorithms, which are a set of parametric algebraic equations, use a set of measurements to determine whether performance degradation (fault) exists in a chiller. The set of measurements consists of sensing the temperature of the condenser cooling water supply, the temperature of the supply and return lines of the evaporator, and measuring the power supplied by a motor.
The Mathur method is disadvantageous, however, in that the chilled water flow rate is assumed to be constant. This assumption is completely unreliable because there are many factors, such as a clogged strainer, automated control cycling, lowered system demand, or a partially closed valve that can directly affect the flow of the chilled water, thereby rendering the flow rate anything but a constant. Such factors bear directly on the chiller tonnage calculation which is directly related to the chilled water flow rate. Thus, the chiller efficiency, which is a ratio of the design and actual chiller tonnage, cannot be accurately computed.
U.S. Pat. No. 4,161,106 issued to Savage et al. discloses a method and apparatus for determining whether a refrigeration unit (i.e., chiller) is operating efficiently. A correlation is drawn between the refrigeration unit condition and condenser head pressure. That is, the condenser head pressure is compared with an ideal condenser head pressure obtained as a function of load on the compressor motor and either condenser cooling fluid inlet or outlet temperature.
The approach of Savage et al. is also disadvantageous in that it does not compute the actual rate of flow of the chilled water. Rather, the flow rate is indirectly calculated by measuring the compressor motor load and assuming that the flow rate is a certain function thereof. Further, Savage et al. does not disclose a means of providing the operator with a report of the critical parameters, making it difficult for the operator to evaluate the chiller's performance.